July 19, 2007

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.

Kilauea update: An eruptive sequel with a new twist?

Leading tip of the fissure (steaming area at bottom of photo) that erupted lava minutes after photo was taken.

Volcano watchers, like recent movie-goers, are enjoying another summer sequel. Amidst new renditions of popular flicks like Spiderman, Pirates, Harry Potter, and Rush Hour, it seems that "Die Hard IV" would be a better name for the show featured at Kilauea.

Viewers of the Pu`u `O`o crater webcam (http://hvo.wr.usgs.gov/cam/) are witnessing a benchmark event in the Pu`u `O`o-Kupaianaha eruptive era of Kilauea Volcano (January 1983 to present). A new "episode" of this eruption is being ushered in at vents within and adjacent to Pu`u `O`o. We know from experience that these transitional periods in eruptive activity warrant careful study and a vigilant watch.

As reported in the last two Volcano Watch columns, the sequence of events that began on Father's Day (June 17) 2007 continues to mimic the volcano's behavior leading up to, and following, the January 1997 fissure eruptions in Napau Crater, 4 km uprift (northwest) of Pu`u `O`o.

In both events, a disruption along the subsurface pathway feeding magma from beneath the summit to the Pu`u `O`o vent area resulted in a small eruption of lava at a new location. In both cases, magma was drawn from either end of the conduit toward the new eruption site, causing deflation of the summit and collapse of the Pu`u `O`o crater.

Just as a skylight in an active lava tube provides a way to sample lava during its transport from the vent, these uprift eruptions are samples from the magmatic plumbing system between the summit reservoir and Pu`u `O`o.

Despite all their geophysical and circumstantial similarities, the relative temperature, composition, and mix of crystals in lava erupted before and during both the Napau and Kane Nui o Hamo events was distinctly different.

Before January 1997, lava erupted from Pu`u `O`o was consistently hot (up to 1,160 degrees Centigrade or 2,100 degrees Fahrenheit), and crystals in the lava were almost exclusively grown from the magma during its transit from the summit. Careful analysis showed that 1997 Napau lava was created by a mixture of Pu`u `O`o magma with older and much cooler crystal mushes left over from 1963 and 1968 Napau eruptions.

Before June 2007, the lava erupting from Pu`u `O`o vents was consistently 15 to 20 degrees Centigrade cooler than it was a decade earlier. Over the last several years, lava from Pu`u `O`o vents has contained a mix of crystals whose chemistry indicates that hotter magma from the summit was contaminated with cooler stagnant magma shortly before erupting at Pu`u `O`o.

In further contrast to the situation in 1997, the smaller amount of new lava erupted at Kane Nui o Hamo in June 2007 was significantly hotter (1,160 degrees Centigrade or 2,100 degrees Fahrenheit). Our preliminary analyses identify this to be the higher temperature component that has fed and mixed with a cooler stagnant magma in a shallow reservoir beneath the vicinity of the Pu`u `O`o vent for the last several years.

These differences are interesting but probably not significant enough to change the course of the eruption in 2007 and keep it from following the script of events played out in 1997.

As we watch the collapsed crater refill with lava now, so did we watch it a decade ago. The lava pond repeatedly rose from within the crater and breached the northwest and southeast crater rim. Some video cameras stationed on the crater's edge recorded their own demise (see http://hvo.wr.usgs.gov/products/OF97537/). The 1997 events were the first time since 1986 that lava overflowed from inside Pu`u `O`o. A repeat performance might be in the offing.

It seems likely that a new lava flow field will once again emerge from the vicinity of the Pu`u `O`o vents as in 1997. The newest and most interesting twist in this encore eruptive performance will likely be where and how fast the lava spreads from its source. Tune in next week for the latest in this developing story from our ongoing monitoring efforts.

Activity update

This past week, activity levels at the summit of Kilauea Volcano remained low. Seismic tremor levels remain low; earthquakes continue to be concentrated in the upper east rift zone. The summit caldera continues to inflate.

There is no active lava anywhere on the surface except within the Pu`u `O`o crater. Since July 13, the lava lake has drained, the east vent has weakened, and the west vent has become the most active. New vents have opened in the West Gap pit that now feed an active lava lake. In the past few days, vents have also opened within Puka Nui pit and high on the south wall of the crater. Since July 10, the interior of the crater, including the floor and debris at the base of the walls, has been rising dramatically.

Four earthquakes beneath Hawai`i Island were reported felt within the past week. A magnitude-2.7 earthquake occurred at 9:40 a.m. H.s.t. on Saturday, July 14, and was located 3 km (2 miles) northwest of Ho`okena at a depth of 14 km (9 miles). A magnitude-3.2 earthquake occurred at 1:56 a.m. on Monday, July 16, and was located 8 km (4 miles) southeast of Pu`u `O`o crater at a depth of 10 km (6 miles). A magnitude-2.5 earthquake occurred at 00:56 a.m. on Tuesday, July 17, and was located 5 km (3 miles) south of Volcano Village at a depth of 3 km (2 miles). A magnitude-2.8 earthquake occurred at 11:41 a.m. on the same day and was located 4 km (3 miles) southeast of Kilauea summit at a depth of 3 km (2 miles).

Mauna Loa is not erupting. One earthquake was located beneath the summit. Extension between locations spanning the summit, indicating inflation, continues at steady, slow rates, which have slowed further since May 2007.